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[DPRG] stella driving down a path

Subject: [DPRG] stella driving down a path
From: Chris Jang cjang at ix.netcom.com
Date: Sat May 12 08:39:49 CDT 2007

Thanks - my mom asked me why Stella drove off the path. It is
a good question and deserving of an answer. I think the answer
is interesting as it is visually obvious.


Improvements to any one of the following will prevent this failure.

1. more reliable and higher framerate camera system
2. more sophisticated computer vision algorithms
3. a real control system with a model of the environment

Number 1 is constrained by the hardware. That is for the next robot.

Number 2 is applying what I already know. Like Stanford's robot, I
think Stella will have to use statistical methods. Even with a
multi-million dollar robot like Stanley, there was a point beyond
which improving the hardware to eliminate noise was too expensive.
So it had to be done in software.

Number 3 is stuff I need to learn. Stella needs to have an adaptive
control strategy. This also implies a re-architecture of the
software into a modular form. At this point, I may move the higher
level code into C++. However, the low-level code will remain in C.
And the user interface code for the LCD, pushbutton and radio is in
the Lua scripting language. I am trying to use the optimal level of
abstraction for different problems.

-----Original Message-----
>From: Charles Thurston <cthurston at sc.rr.com>
>Sent: May 12, 2007 7:47 AM
>To: dprglist at dprg.org
>Subject: Re: [DPRG] stella driving down a path
>Hello Chris,
>Friday, May 11, 2007, 9:35:17 PM, you wrote:
>> http://golem5.org/video/mvi4027.mpg
>> Hello Everyone,
>> Here is Stella again. There are no changes to the simple
>> obstacle avoidance algorithm from the last movie in a
>> parking lot. What's going on is purely reactive behavior.
>> There is no path planning or kinematic model.
>> Note that Stella has no sensors other than a USB webcam
>> running at around 1.3 frames per second.
>> It looks interesting but really there is a lot of work to
>> do. The computer vision is the simplest possible - look
>> for a clear patch of ground immediately ahead - and
>> ignores a lot that is useful. There is also no control
>> model. I just picked constant thresholds and duty cycles
>> for sensing obstacles and driving the motors. It is
>> entirely ad hoc and does not adapt at all. That's why
>> Stella over-corrects. A real control system is necessary.
>> By the end of the year, it will probably be necessary to
>> move on to another robot. That will probably be a hobby-
>> grade RC vehicle with at least 10x the computer power.
>> Chris
>> _______________________________________________
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>Best regards,
> Charles                            mailto:cthurston at sc.rr.com
>DPRGlist mailing list
>DPRGlist at dprg.org

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